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ALTER INDEX (Transact-SQL)

Modifies an existing table or view index (relational or XML) by disabling, rebuilding, or reorganizing the index, or by setting options on the index.

Topic link icon Transact-SQL Syntax Conventions


ALTER INDEX { index_name | ALL }
    ON <object>
    { REBUILD 
        [ [ WITH ( <rebuild_index_option> [ ,...n ] ) ] 
          | [ PARTITION = partition_number 
                [ WITH ( <single_partition_rebuild_index_option>
                        [ ,...n ] )
                ] 
            ]
        ]
    | DISABLE
    | REORGANIZE 
        [ PARTITION = partition_number ]
        [ WITH ( LOB_COMPACTION = { ON | OFF } ) ]
    | SET ( <set_index_option> [ ,...n ] ) 
    }
[ ; ]

<object> ::=
{
    [ database_name. [ schema_name ] . | schema_name. ]
        table_or_view_name
}

<rebuild_index_option > ::=
{
    PAD_INDEX  = { ON | OFF }
  | FILLFACTOR = fillfactor 
  | SORT_IN_TEMPDB = { ON | OFF }
  | IGNORE_DUP_KEY = { ON | OFF }
  | STATISTICS_NORECOMPUTE = { ON | OFF }
  | ONLINE = { ON | OFF } 
  | ALLOW_ROW_LOCKS = { ON | OFF }
  | ALLOW_PAGE_LOCKS = { ON | OFF }
  | MAXDOP = max_degree_of_parallelism
}

<single_partition_rebuild_index_option> ::=
{
    SORT_IN_TEMPDB = { ON | OFF }
  | MAXDOP = max_degree_of_parallelism
}

<set_index_option>::=
{
    ALLOW_ROW_LOCKS= { ON | OFF }
  | ALLOW_PAGE_LOCKS = { ON | OFF }
  | IGNORE_DUP_KEY = { ON | OFF }
  | STATISTICS_NORECOMPUTE = { ON | OFF }
}
index_name

Is the name of the index. Index names must be unique within a table or view but do not have to be unique within a database. Index names must follow the rules of identifiers.

ALL

Specifies all indexes associated with the table or view regardless of the index type. Specifying ALL causes the statement to fail if one or more indexes are in an offline or read-only filegroup or the specified operation is not allowed on one or more index types. The following table lists the index operations and disallowed index types.

Specifying ALL with this operation Fails if the table has one or more

REBUILD WITH ONLINE = ON

XML index

Large object data type columns: image, text, ntext, varchar(max), nvarchar(max), varbinary(max), and xml

REBUILD PARTITION = partition_number

Nonpartitioned index, XML index, or disabled index

REORGANIZE

Indexes with ALLOW_PAGE_LOCKS set to OFF

REORGANIZE PARTITION = partition_number

Nonpartitioned index, XML index, or disabled index

SET

Disabled index

If ALL is specified with PARTITION = partition_number, all indexes must be aligned. This means that they are partitioned based on equivalent partition functions. Using ALL with PARTITION causes all index partitions with the same partition_number to be rebuilt or reorganized. For more information about partitioned indexes, see Partitioned Tables and Indexes.

database_name

Is the name of the database.

schema_name

Is the name of the schema to which the table or view belongs.

table_or_view_name

Is the name of the table or view associated with the index. To display a report of the indexes on an object, use the sys.indexes catalog view.

REBUILD [ WITH (<rebuild_index_option> [ ,... n]) ]

Specifies the index will be rebuilt using the same columns, index type, uniqueness attribute, and sort order. This clause is equivalent to DBCC DBREINDEX. REBUILD enables a disabled index. Rebuilding a clustered index does not rebuild associated nonclustered indexes unless the keyword ALL is specified. If index options are not specified, the existing index option values stored in sys.indexes are applied. For any index option whose value is not stored in sys.indexes, the default indicated in the argument definition of the option applies.

The options ONLINE and IGNORE_DUP_KEY are not valid when you rebuild an XML index.

If ALL is specified and the underlying table is a heap, the rebuild operation has no effect on the table. Any nonclustered indexes associated with the table are rebuilt.

The rebuild operation can be minimally logged if the database recovery model is set to either bulk-logged or simple. For more information, see Choosing a Recovery Model for Index Operations.

ms188388.note(en-US,SQL.90).gifNote:
When you rebuild a primary XML index, the underlying user table is unavailable for the duration of the index operation.

PARTITION

Specifies that only one partition of an index will be rebuilt or reorganized. PARTITION cannot be specified if index_name is not a partitioned index.

partition_number

Is the partition number of a partitioned index that is to be rebuilt or reorganized. partition_number is a constant expression that can reference variables. These include user-defined type variables or functions and user-defined functions, but cannot reference a Transact-SQL statement. partition_number must exist or the statement fails.

WITH (<single_partition_rebuild_index_option>)

SORT_IN_TEMPDB and MAXDOP are the options that can be specified when you rebuild a single partition (PARTITION = n). XML indexes cannot be specified in a single partition rebuild operation.

Rebuilding a partitioned index cannot be performed online. The entire table is locked during this operation.

DISABLE

Marks the index as disabled and unavailable for use by the SQL Server 2005 Database Engine. Any index can be disabled. The index definition of a disabled index remains in the system catalog with no underlying index data. Disabling a clustered index prevents user access to the underlying table data. To enable an index, use ALTER INDEX REBUILD or CREATE INDEX WITH DROP_EXISTING. For more information, see Disabling Indexes.

REORGANIZE

Specifies the index leaf level will be reorganized. This clause is equivalent to DBCC INDEXDEFRAG. ALTER INDEX REORGANIZE statement is always performed online. This means long-term blocking table locks are not held and queries or updates to the underlying table can continue during the ALTER INDEX REORGANIZE transaction. REORGANIZE cannot be specified for a disabled index or an index with ALLOW_PAGE_LOCKS set to OFF.

WITH ( LOB_COMPACTION = { ON | OFF } )

Specifies that all pages that contain large object (LOB) data are compacted. The LOB data types are image, text, ntext, varchar(max), nvarchar(max), varbinary(max), and xml. Compacting this data can improve disk space use. The default is ON.

ON

All pages that contain large object data are compacted.

Reorganizing a specified clustered index compacts all LOB columns that are contained in the clustered index. Reorganizing a nonclustered index compacts all LOB columns that are nonkey (included) columns in the index. For more information, see Creating Indexes with Included Columns.

When ALL is specified, all indexes that are associated with the specified table or view are reorganized, and all LOB columns that are associated with the clustered index, underlying table, or nonclustered index with included columns are compacted.

OFF

Pages that contain large object data are not compacted.

OFF has no effect on a heap.

The LOB_COMPACTION clause is ignored if LOB columns are not present.

SET ( <set_index option> [ ,... n] )

Specifies index options without rebuilding or reorganizing the index. SET cannot be specified for a disabled index.

PAD_INDEX = { ON | OFF }

Specifies index padding. The default is OFF.

ON

The percentage of free space that is specified by FILLFACTOR is applied to the intermediate-level pages of the index. If FILLFACTOR is not specified at the same time PAD_INDEX is set to ON, the fill factor value stored in sys.indexes is used.

OFF or fillfactor is not specified

The intermediate-level pages are filled to near capacity. This leaves sufficient space for at least one row of the maximum size that the index can have, based on the set of keys on the intermediate pages.

For more information, see CREATE INDEX (Transact-SQL).

FILLFACTOR = fillfactor

Specifies a percentage that indicates how full the Database Engine should make the leaf level of each index page during index creation or alteration. fillfactor must be an integer value from 1 to 100. The default is 0.

ms188388.note(en-US,SQL.90).gifNote:
Fill factor values 0 and 100 are the same in all respects.

An explicit FILLFACTOR setting applies only when the index is first created or rebuilt. The Database Engine does not dynamically keep the specified percentage of empty space in the pages. For more information, see CREATE INDEX (Transact-SQL).

To view the fill factor setting, use sys.indexes.

ms188388.note(en-US,SQL.90).gifImportant:
Creating or altering a clustered index with a FILLFACTOR value affects the amount of storage space the data occupies, because the Database Engine redistributes the data when it creates the clustered index.

SORT_IN_TEMPDB = { ON | OFF }

Specifies whether to store the sort results in tempdb. The default is OFF.

ON

The intermediate sort results that are used to build the index are stored in tempdb. If tempdb is on a different set of disks than the user database, this may reduce the time needed to create an index. However, this increases the amount of disk space that is used during the index build.

OFF

The intermediate sort results are stored in the same database as the index.

If a sort operation is not required, or if the sort can be performed in memory, the SORT_IN_TEMPDB option is ignored.

For more information, see tempdb and Index Creation.

IGNORE_DUP_KEY = { ON | OFF }

Specifies the error response to duplicate key values in a multiple-row insert transaction on a unique clustered or unique nonclustered index. The default is OFF.

ON

A warning message is issued, and only the rows that violate the UNIQUE index fail.

OFF

An error message is issued, and the whole transaction is rolled back.

The IGNORE_DUP_KEY setting applies only to insert operations that occur after the index is created or rebuilt. The setting has no affect during the index operation. IGNORE_DUP_KEY has no effect in an UPDATE statement.

IGNORE_DUP_KEY cannot be set to ON for XML indexes and indexes created on a view. For more information, see CREATE INDEX (Transact-SQL).

STATISTICS_NORECOMPUTE = { ON | OFF }

Specifies whether distribution statistics are recomputed. The default is OFF.

ON

Out-of-date statistics are not automatically recomputed.

OFF

Automatic statistics updating are enabled.

To restore automatic statistics updating, set the STATISTICS_NORECOMPUTE to OFF, or execute UPDATE STATISTICS without the NORECOMPUTE clause.

ms188388.note(en-US,SQL.90).gifImportant:
Disabling automatic recomputation of distribution statistics may prevent the query optimizer from picking optimal execution plans for queries that involve the table.

ONLINE = { ON | OFF }

Specifies whether underlying tables and associated indexes are available for queries and data modification during the index operation. The default is OFF.

ms188388.note(en-US,SQL.90).gifNote:
Online index operations are available only in SQL Server 2005 Enterprise Edition.

ON

Long-term table locks are not held for the duration of the index operation. During the main phase of the index operation, only an Intent Share (IS) lock is held on the source table. This allows queries or updates to the underlying table and indexes to continue. At the start of the operation, a Shared (S) lock is very briefly held on the source object. At the end of the operation, an S lock is very briefly held on the source if a nonclustered index is being created, or an SCH-M (Schema Modification) lock is acquired when a clustered index is created or dropped online, or when a clustered or nonclustered index is being rebuilt. ONLINE cannot be set to ON when an index is being created on a local temporary table.

OFF

Table locks are applied for the duration of the index operation. An offline index operation that creates, rebuilds, or drops a clustered index, or rebuilds or drops a nonclustered index, acquires a Schema modification (Sch-M) lock on the table. This prevents all user access to the underlying table for the duration of the operation. An offline index operation that creates a nonclustered index acquires a Shared (S) lock on the table. This prevents updates to the underlying table but allows read operations, such as SELECT statements.

For more information, see How Online Index Operations Work. For more information about locks, see Lock Modes.

Indexes, including indexes on global temp tables, can be rebuilt online with the following exceptions:

  • Disabled indexes
  • XML indexes
  • Indexes on local temp tables
  • Partitioned indexes
  • Clustered indexes if the underlying table contains LOB data types
  • Nonclustered indexes that are defined with LOB data type columns

Nonclustered indexes can be rebuilt online if the table contains LOB data types but none of these columns are used in the index definition as either key or nonkey columns.

ALLOW_ROW_LOCKS = { ON | OFF }

Specifies whether row locks are allowed. The default is ON.

ON

Row locks are allowed when accessing the index. The Database Engine determines when row locks are used.

OFF

Row locks are not used.

ALLOW_PAGE_LOCKS = { ON | OFF }

Specifies whether page locks are allowed. The default is ON.

ON

Page locks are allowed when you access the index. The Database Engine determines when page locks are used.

OFF

Page locks are not used.

ms188388.note(en-US,SQL.90).gifNote:
An index cannot be reorganized when ALLOW_PAGE_LOCKS is set to OFF.

MAXDOP = max_degree_of_parallelism

Overrides the max degree of parallelism configuration option for the duration of the index operation. For more information, see max degree of parallelism Option. Use MAXDOP to limit the number of processors used in a parallel plan execution. The maximum is 64 processors.

max_degree_of_parallelism can be:

1

Suppresses parallel plan generation.

>1

Restricts the maximum number of processors used in a parallel index operation to the specified number.

0 (default)

Uses the actual number of processors or fewer based on the current system workload.

For more information, see Configuring Parallel Index Operations.

ms188388.note(en-US,SQL.90).gifNote:
Parallel index operations are available only in SQL Server 2005 Enterprise Edition.

ALTER INDEX cannot be used to repartition an index or move it to a different filegroup. This statement cannot be used to modify the index definition, such as adding or deleting columns or changing the column order. Use CREATE INDEX with the DROP_EXISTING clause to perform these operations.

When an option is not explicitly specified, the current setting is applied. For example, if a FILLFACTOR setting is not specified in the REBUILD clause, the fill factor value stored in the system catalog will be used during the rebuild process. To view the current index option settings, use sys.indexes.

ms188388.note(en-US,SQL.90).gifNote:
The values for ONLINE, MAXDOP, and SORT_IN_TEMPDB are not stored in the system catalog. Unless specified in the index statement, the default value for the option is used.

On multiprocessor computers, just like other queries do, ALTER INDEX REBUILD automatically uses more processors to perform the scan and sort operations that are associated with modifying the index. When you run ALTER INDEX REORGANIZE, with or without LOB_COMPACTION, the max degree of parallelism value is a single threaded operation. For more information, see Configuring Parallel Index Operations.

An index cannot be reorganized or rebuilt if the filegroup in which it is located is offline or set to read-only. When the keyword ALL is specified and one or more indexes are in an offline or read-only filegroup, the statement fails.

Rebuilding Indexes

Rebuilding an index drops and re-creates the index. This removes fragmentation, reclaims disk space by compacting the pages based on the specified or existing fill factor setting, and reorders the index rows in contiguous pages. When ALL is specified, all indexes on the table are dropped and rebuilt in a single transaction. FOREIGN KEY constraints do not have to be dropped in advance. When indexes with 128 extents or more are rebuilt, the Database Engine defers the actual page deallocations, and their associated locks, until after the transaction commits. For more information, see Dropping and Rebuilding Large Objects.

ms188388.note(en-US,SQL.90).gifNote:
In general, rebuilding or reorganizing small indexes often does not reduce fragmentation. The pages of small indexes are stored on mixed extents. Mixed extents are shared by up to eight objects, so fragmentation in a small index might not be reduced after reorganizing or rebuilding the index. For more information about mixed extents, see Pages and Extents.

In earlier versions of SQL Server, you could sometimes rebuild a nonclustered index to correct inconsistencies caused by hardware failures. In SQL Server 2005, you may still be able to repair such inconsistencies between the index and the clustered index by rebuilding a nonclustered index offline. However, you cannot repair nonclustered index inconsistencies by rebuilding the index online, because the online rebuild mechanism will use the existing nonclustered index as the basis for the rebuild and thus persist the inconsistency. Rebuilding the index offline, by contrast, will force a scan of the clustered index (or heap) and so remove the inconsistency. As with earlier versions, we recommend recovering from inconsistencies by restoring the affected data from a backup; however, you may be able to repair the index inconsistencies by rebuilding the nonclustered index offline. For more information, see DBCC CHECKDB (Transact-SQL).

Reorganizing Indexes

Reorganizing an index uses minimal system resources. It defragments the leaf level of clustered and nonclustered indexes on tables and views by physically reordering the leaf-level pages to match the logical, left to right, order of the leaf nodes. Reorganizing also compacts the index pages. Compaction is based on the existing fill factor value. To view the fill factor setting, use sys.indexes.

When ALL is specified, relational indexes, both clustered and nonclustered, and XML indexes on the table are reorganized. Some restrictions apply when specifying ALL, see the definition for ALL in the Arguments section.

For more information, see Reorganizing and Rebuilding Indexes.

Disabling Indexes

Disabling an index prevents user access to the index, and for clustered indexes, to the underlying table data. The index definition remains in the system catalog. Disabling a nonclustered index or clustered index on a view physically deletes the index data. Disabling a clustered index prevents access to the data, but the data remains unmaintained in the B-tree until the index is dropped or rebuilt. To view the status of an enabled or disabled index, query the is_disabled column in the sys.indexes catalog view.

If a table is in a transactional replication publication, you cannot disable any indexes that are associated with primary key columns. These indexes are required by replication. To disable an index, you must first drop the table from the publication. For more information, see Publishing Data and Database Objects.

Use the ALTER INDEX REBUILD statement or the CREATE INDEX WITH DROP_EXISTING statement to enable the index. Rebuilding a disabled clustered index cannot be performed with the ONLINE option set to ON. For more information, see Disabling Indexes.

Setting Options

You can set the options ALLOW_ROW_LOCKS, ALLOW_PAGE_LOCKS, IGNORE_DUP_KEY and STATISTICS_NORECOMPUTE for a specified index without rebuilding or reorganizing that index. The modified values are immediately applied to the index. To view these settings, use sys.indexes. For more information, see Setting Index Options.

Row and Page Locks Options

When ALLOW_ROW_LOCKS = ON and ALLOW_PAGE_LOCK = ON, row-level, page-level, and table-level locks are allowed when you access the index. The Database Engine chooses the appropriate lock and can escalate the lock from a row or page lock to a table lock.

When ALLOW_ROW_LOCKS = OFF and ALLOW_PAGE_LOCK = OFF, only a table-level lock is allowed when you access the index. For more information about configuring the locking granularity for an index, see Customizing Locking for an Index.

If ALL is specified when the row or page lock options are set, the settings are applied to all indexes. When the underlying table is a heap, the settings are applied in the following ways:

ALLOW_ROW_LOCKS = ON or OFF

To the heap and any associated nonclustered indexes.

ALLOW_PAGE_LOCKS = ON

To the heap and any associated nonclustered indexes.

ALLOW_PAGE_LOCKS = OFF

Fully to the nonclustered indexes. This means that all page locks are not allowed on the nonclustered indexes. On the heap, only the shared (S), update (U) and exclusive (X) locks for the page are not allowed. The Database Engine can still acquire an intent page lock (IS, IU or IX) for internal purposes.

For more information, see Lock Escalation (Database Engine).

Online Index Operations

When rebuilding an index and the ONLINE option is set to ON, the underlying objects, the tables and associated indexes, are available for queries and data modification. Exclusive table locks are held only for a very short amount of time during the alteration process.

Reorganizing an index is always performed online. The process does not hold locks long term and, therefore, does not block queries or updates that are running.

You can perform concurrent online index operations on the same table only when doing the following:

  • Creating multiple nonclustered indexes.
  • Reorganizing different indexes on the same table.
  • Reorganizing different indexes while rebuilding nonoverlapping indexes on the same table.

All other online index operations performed at the same time fail. For example, you cannot rebuild two or more indexes on the same table concurrently, or create a new index while rebuilding an existing index on the same table.

For more information, see Performing Index Operations Online.

To execute ALTER INDEX, at a minimum, ALTER permission on the table or view is required.

A. Rebuilding an index

The following example rebuilds a single index on the Employee table.

USE AdventureWorks;
GO
ALTER INDEX PK_Employee_EmployeeID ON HumanResources.Employee
REBUILD;
GO

B. Rebuilding all indexes on a table and specifying options

The following example specifies the keyword ALL. This rebuilds all indexes associated with the table. Three options are specified.

USE AdventureWorks;
GO
ALTER INDEX ALL ON Production.Product
REBUILD WITH (FILLFACTOR = 80, SORT_IN_TEMPDB = ON,
              STATISTICS_NORECOMPUTE = ON);
GO

C. Reorganizing an index with LOB compaction

The following example reorganizes a single clustered index. Because the index contains a LOB data type in the leaf level, the statement also compacts all pages that contain the large object data. Note that specifying the WITH (LOB_COMPACTION) option is not required because the default value is ON.

USE AdventureWorks;
GO
ALTER INDEX PK_ProductPhoto_ProductPhotoID ON Production.ProductPhoto
REORGANIZE ;
GO

D. Setting options on an index

The following example sets several options on the index AK_SalesOrderHeader_SalesOrderNumber.

USE AdventureWorks;
GO
ALTER INDEX AK_SalesOrderHeader_SalesOrderNumber ON
    Sales.SalesOrderHeader
SET (
    STATISTICS_NORECOMPUTE = ON,
    IGNORE_DUP_KEY = ON,
    ALLOW_PAGE_LOCKS = ON
    ) ;
GO

E. Disabling an index

The following example disables a nonclustered index on the Employee table.

USE AdventureWorks;
GO
ALTER INDEX IX_Employee_ManagerID ON HumanResources.Employee
DISABLE ;
GO

F. Disabling constraints

The following example disables a PRIMARY KEY constraint by disabling the PRIMARY KEY index. The FOREIGN KEY constraint on the underlying table is automatically disabled and warning message is displayed.

USE AdventureWorks;
GO
ALTER INDEX PK_Department_DepartmentID ON HumanResources.Department
DISABLE ;
GO

The result set returns this warning message.

Warning: Foreign key 'FK_EmployeeDepartmentHistory_Department_DepartmentID' on table 'EmployeeDepartmentHistory' referencing table 'Department' was disabled as a result of disabling the index 'PK_Department_DepartmentID'.

G. Enabling constraints

The following example enables the PRIMARY KEY and FOREIGN KEY constraints that were disabled in Example F.

The PRIMARY KEY constraint is enabled by rebuilding the PRIMARY KEY index.

USE AdventureWorks;
GO
ALTER INDEX PK_Department_DepartmentID ON HumanResources.Department
REBUILD ;
GO

The FOREIGN KEY constraint is then enabled.

ALTER TABLE HumanResources.EmployeeDepartmentHistory
CHECK CONSTRAINT FK_EmployeeDepartmentHistory_Department_DepartmentID;
GO

H. Rebuilding a partitioned index

The following example rebuilds a single partition, partition number 5, of the partitioned index IX_TransactionHistory_TransactionDate. This example assumes the partitioned index sample has been installed. For installation information, see Readme_PartitioningScript.

USE AdventureWorks;
GO
-- Verify the partitioned indexes.
SELECT *
FROM sys.dm_db_index_physical_stats (DB_ID(),OBJECT_ID(N'Production.TransactionHistory'), NULL , NULL, NULL);
GO
--Rebuild only partition 5.
ALTER INDEX IX_TransactionHistory_TransactionDate
ON Production.TransactionHistory
REBUILD Partition = 5;
GO
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